JP2000249525A - Inclined incidence interferometer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To observe interference fringes with different sensitivity by using a plurality of sets of diffraction grating providing a specific selection means of light flux for interference fringe observation with different grating constants in the case of a return mirror reversing light flux for observing interference fringes. SOLUTION: A first and a second diffraction gratings 12 and 14 are constituted of two sets of gratings 12A, 12B, 14A and 14B with different grating constants to obtain light fluxes A and B for interference fringe observation with different measurement sensitivity. In front of a return mirror 26 for reversing the light fluxes A and B for interference fringe observation provided on a focusing optical system 20 for forming interference fringes on an interference fringe observation screen 18, a selection means 30 of light flux for interference fringe observation is provided. One of the light fluxes A and B for interference fringe observation is introduced in the return mirror 26 and on an interference fringe observation screen 18, only the interference fringes by selected one light flux for interference fringe observation is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grazing incidence interferometer having a folding mirror for reversing a light beam for observing interference fringes.

[0002]

2. Description of the Related Art Conventionally, an oblique incidence interferometer device capable of measuring the surface shape of a test surface having a certain degree of unevenness by lowering measurement sensitivity by obliquely incident coherent light on the test surface. It has been known.

FIG. 8 shows a typical configuration of the oblique incidence interferometer.

In this oblique incidence interferometer, the coherent light is made incident on a wavefront splitting means 102 to split the wavefront in two directions. Is the object light, and the other light beam is the reference light. The object light and the reference light are made incident on the wavefront synthesizing means 104 to be wavefront-synthesized, and the object light and the reference light emitted from the wavefront synthesizing means 104 in the same direction. An interference fringe generated by optical interference with light is imaged by the television camera 108 via the imaging lens 106, and the surface 2a to be inspected is determined based on the interference fringe image.
Is to be measured.

[0005]

However, in the above-described conventional oblique incidence interferometer apparatus, since the optical path length from each position of the surface 2a to be inspected to the imaging lens 106 is different, the interference image picked up by the television camera 108 is taken. There is a problem that trapezoidal distortion occurs in the stripe image, and the shape measurement of the test surface 2a cannot be accurately performed.

On the other hand, as shown in FIG.
If the interference fringe observation screen 110 is arranged at a position conjugate with a, and the interference fringe image formed on the interference fringe observation screen 110 is captured by the television camera 108,
It is possible to prevent trapezoidal distortion from occurring in the interference fringe image. In the figure, the imaging lens 106 is
The focal point is arranged so as to be located on the surface 2a to be inspected, a collimator lens 112 is arranged afocally with the imaging lens 106, and an interference fringe observation screen 110 is arranged at the second focal position.

When such a configuration is adopted,
As shown in FIG. 10, a folding mirror 114 is provided at the second focal position of the imaging lens 106 to reverse the light beam for interference fringe observation, and a half mirror is provided between the imaging lens 106 and the wavefront synthesizing means 104. If the interference fringe observation screen 110 is provided in the deflected reflection optical path and the interference fringe observation screen 110 is provided, it is possible to prevent the total length of the interferometer device from becoming long.

By the way, the interference fringe image formed on the interference fringe observation screen 110 is transmitted to the television camera 108.
If the interference fringes can be observed with different sensitivities in the case of imaging with, the surface shape of the test surface 2a can be measured more accurately.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in an oblique incidence interferometer apparatus provided with a folding mirror for reversing a light beam for interference fringe observation, observation of interference fringes with different sensitivities. It is an object of the present invention to provide a grazing incidence interferometer device capable of performing the following.

[0010]

The present invention achieves the above object by using a plurality of sets of diffraction gratings having different grating constants and providing a predetermined light beam selecting means for observing interference fringes. is there.

That is, in the oblique incidence interferometer according to the present invention, the coherent light is made incident on the wavefront splitting means to split the wavefront in two directions, and one light beam is obliquely incident on the surface to be measured. The reflected light is used as the object light and the other light beam is used as the reference light. The object light and the reference light are made incident on the wavefront synthesizing means for wavefront synthesis, and the object light emitted from the wavefront synthesizing means in the same direction. And in the oblique incidence interferometer device configured to form an interference fringe caused by optical interference with the reference light on the interference fringe observation screen, an imaging optical system that forms the interference fringe on the interference fringe observation screen, A folding mirror for reversing the light beam for interference fringe observation emitted in the same direction, and a first and a second mirror provided between the folding mirror and the wavefront combining means on the surface to be measured and the folding mirror. An imaging lens provided so as to position a point, and a half mirror provided between the imaging lens and the wavefront synthesizing means and deflecting and reflecting at least a part of the backward traveling light from the folding mirror. Wherein the interference fringe observation screen is disposed at a position conjugate with the test surface in the deflecting and reflecting optical path from the half mirror, and the wavefront dividing means and the wavefront synthesizing means have a lattice constant It comprises a plurality of different sets of diffraction gratings, and selectively selects only a light beam for interference fringe observation formed by a diffraction grating having a predetermined lattice constant among the plurality of sets of diffraction gratings on the imaging lens side of the folding mirror. A light beam selecting means for observing interference fringes to be transmitted is provided.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described. FIG. 1 shows an oblique incidence interferometer device 10 according to this embodiment.
FIG. 2 is a plan view of FIG.

As shown in these figures, the oblique incidence interferometer device 10 is provided at a position below the center of first and second diffraction gratings 12 and 14 which are opposed to each other at a predetermined interval in the horizontal direction. Is a birch type oblique incidence interferometer device provided with an object support member 16 for supporting the coherent light, which is emitted from a light source (not shown) and is converted into parallel light by a first diffraction grating 12 (wavefront splitting means). ) To split the wavefront into a plurality of diffracted lights, make the + 1st-order diffracted light obliquely incident on the test surface 2a of the subject 2, make the reflected light the object light, and use the 0th-order diffracted light as the reference light. The object light and the reference light are made incident on the second diffraction grating 14 (wavefront synthesizing means) to perform wavefront synthesis.

In the oblique incidence interferometer apparatus 10, interference fringes generated by optical interference between the 0th-order diffracted light of the object light and the -1st-order diffracted light of the reference light emitted obliquely upward from the second diffraction grating 14 are generated. The interference fringe observation screen 18 is formed by the imaging optical system 20.

The first diffraction grating 12 includes a diffraction grating 12A having a small lattice constant and a diffraction grating 12B having a large lattice constant, and + 1st-order diffracted light from each of the diffraction gratings 12A and 12B is incident on the surface 2a to be measured. So that the diffraction grating 1
It is provided in two upper and lower stages with 2A facing up. On the other hand, the second
The diffraction grating 14 includes a diffraction grating 14A having a small lattice constant and a diffraction grating 14B having a large lattice constant.
The object light and reference light from 2A are incident on the diffraction grating 14A, and the object light and reference light from the diffraction grating 12B are incident on the diffraction grating 14B. .

Since the diffraction grating 12A having a small grating constant has a large diffraction angle, the angle of incidence of the + 1st-order diffracted light on the test surface 2a is small, and the light beam for observing interference fringes (ie, the object beam) emitted from the diffraction grating 14A. The measurement sensitivity of the interference fringe formed by the light beam (A) composed of the 0th-order diffracted light of the light and the -1st-order diffracted light of the reference light increases. On the other hand, since the diffraction grating 12B having a large lattice constant has a small diffraction angle, the angle of incidence of the + 1st-order diffracted light on the test surface 2a increases, and the diffraction grating 1B
The measurement sensitivity of interference fringes formed by the interference fringe observation light beam B emitted from 4B is reduced.

The imaging optical system 20 includes an imaging lens 22
, A deflecting mirror 24, a folding mirror 26, and a polarizing half mirror 28 (half mirror).

The imaging lens 22 is a biconvex lens having a first focal length and a second focal length equal to each other. , B in the optical path.

The deflecting mirror 24 is provided on the image plane side of the imaging lens 22, and deflects and reflects the light beams A and B for observing interference fringes vertically downward.

Further, the folding mirror 26 is provided upward so as to be located at the second focal point of the imaging lens 22, and reverses the light beams A and B for observing interference fringes. However, these interference fringe observation light fluxes A,
B is such that only one of them can enter the turning mirror 26 by the interference fringe observation light beam selecting means 30.

The light beam selecting means 30 for observing interference fringes
A mask member 34 having a window member 32 (light transmitting portion) provided in the vicinity of the folding mirror 26;
Is reciprocated in the direction of the arrow shown in the figure (this will be described later), and the window member 32 is moved to a position where only one of the interference fringe observation light fluxes A and B is transmitted. Thus, the selection of the light beam for interference fringe observation is switched. The window member 32 is 1/4
The window member 32 and the mask member 34 are arranged so as to be non-parallel to the folding mirror 26.

The polarization half mirror 28 is provided between the imaging lens 22 and the second diffraction grating 14 so as to deflect backward reflected light from the folding mirror 20 downward. Since the backward light incident on the polarization half mirror 28 is rotated by 90 ° by the 波長 wavelength plate 32, all the light is deflected and reflected downward without passing through the polarization half mirror 28.

The interference fringe observation screen 18 is arranged at a position conjugate with the test surface 2a in the deflected optical path deflected by the polarization half mirror 28. The interference fringe observation screen 18 includes a light flux A for interference fringe observation,
Among B, only interference fringes are formed by one of the interference fringe observation light fluxes selected by the interference fringe observation light flux selection means 30 (in FIG. 1, the interference fringe observation light flux A is selected). However, an interference fringe image formed on the interference fringe observation screen 18 is captured by a television camera 40 having a CCD image sensor via mirrors 36 and 38.

FIG. 3 is a side sectional view showing the interference fringe observation light beam selecting means 30 in detail. As shown, the interference fringe observation light beam selecting means 30 is housed in a dustproof housing 42 together with the folding mirror 26.

In the dustproof housing 42, a cover member 48 is screwed and fixed to a substrate 44 via a seal member 46. An opening 48 b having substantially the same size as the folding mirror 26 is formed in the upper surface 48 a of the cover member 48.

The turning mirror 26 is provided with a spherical fulcrum member 50 fixed to the substrate 44 so that the turning mirror 26 can be adjusted to an angular position for accurately reversing the light beam for interference fringe observation. It is configured to be able to tilt around. Specifically, folding mirror 2
6 is fixedly screwed to a support plate 54 via a retainer 52, and an upper end of an adjustment screw 56 screwed to the substrate 44 at a plurality of locations abuts on a lower surface of the support plate 54. I have. A tension spring 58 connected to the support plate 54 and the substrate 44 is provided in the vicinity of each adjustment screw 56 so as to hold the folding mirror 26 at an angular position adjusted by the adjustment screw 56. I have.

The mask member 34 constituting the interference fringe observation light beam selecting means 30 is connected to a slider mechanism 60 composed of a solenoid or the like. When the slider mechanism 60 is driven, the lower surface of the upper surface 48a of the cover member 48 is driven. Reciprocate in the direction of the arrow shown in FIG. The cover member 48 is provided with a guide member 62 parallel to the upper surface portion 48a. Incidentally, in FIG.
4 shows a state where the window member 32 has been moved to a position where the window member 32 transmits the light beam A for interference fringe observation.

Next, the operation and effect of this embodiment will be described.

The grazing incidence interferometer device 10 according to this embodiment
The interference fringe observation screen 18 forms interference fringes generated by optical interference between the 0th-order diffracted light of the object light emitted obliquely upward from the second diffraction grating 14 and the -1st-order diffracted light of the reference light. Are the first and second diffraction gratings 12, 1
4 is two sets of diffraction gratings 12A and 12B having different grating constants.
And 14A and 14B, two light beams A and B for observing interference fringes having different measurement sensitivities can be obtained. The oblique incidence interferometer device 10 according to the present embodiment
The image forming optical system 20 for forming the interference fringes on the interference fringe observation screen 18 includes a folding mirror 26 for reversing the light beam for interference fringe observation in order to shorten the entire length of the apparatus. The interference fringe observation light fluxes A and B are provided on the mirror 26 by the interference fringe observation light flux selection means 30.
Only one of them can enter, so that only the interference fringes due to the selected one of the interference fringe observation light fluxes A or B is formed on the interference fringe observation screen 18. . Therefore, by observing the interference fringe image formed on the interference fringe observation screen 18 with the television camera 42, the interference fringes can be observed with different sensitivities, whereby the surface shape of the test surface 2a can be more accurately determined. It becomes possible to measure.

In particular, in this embodiment, the interference fringe observation light beam selecting means 30 comprises a mask member 34 having a window member 32 and a slider mechanism 60 for reciprocating the mask member 34 in the direction of the arrow shown in the figure. Therefore, the selection of the interference fringe observation light fluxes A and B can be switched with a simple configuration.

Further, since the window member 32 is disposed so as to be non-parallel to the folding mirror 26, the light reflected by the window member 32 can be removed from the optical path of the interference fringe observation light beam. Accordingly, it is possible to prevent the reflected light from being incident on the interference fringe observation screen 18 and adversely affecting the measurement of the interference fringes. Further, since the window member 32 is provided at a position distant from the folding mirror 26, it is possible to prevent the adverse effect on interference fringe measurement due to scattered light from dust or the like attached on the window member 32 beforehand. it can. Further, since the window member 32 is formed of a quarter-wave plate, all the backward traveling light from the return mirror 26 can be deflected and reflected downward without passing through the polarization half mirror 28. This can also prevent the adverse effect on the interference fringe measurement.

The oblique incidence interferometer device 10 according to the present embodiment is provided with a deflecting mirror 24 for deflecting and reflecting the light beam for observing interference fringes vertically downward in order to shorten the entire length of the device. The reflecting surface of the mirror 26 faces upward, and foreign matter such as dust is very likely to adhere thereto. However, in the present embodiment, since the mask member 34 is provided above the folding mirror 26, the foreign matter adheres to the folding mirror 26. Prevention can be achieved. In particular, in the present embodiment, since the mask member 34 is also housed in the dustproof housing 42, the dustproof function can be further enhanced.

Further, in this embodiment, since the light beams A and B for observing interference fringes are transmitted by one imaging lens 22, the apparatus can be simplified and the cost can be reduced. . Note that instead of doing this,
An imaging lens may be provided for each of the interference fringe observation light fluxes A and B.

In this embodiment, the case where the image forming optical system 20 is provided with the deflecting mirror 24 has been described. However, as shown by the two-dot chain line in FIG. In this case, if the interference fringe observation light beam selecting means 30 switches the selection of the interference fringe observation light beam incident on the turning mirror 26, the same operation and effect as the present embodiment can be obtained.
Further, in this case, foreign substances such as dust are relatively unlikely to adhere to the reflection surface of the folding mirror 26. Therefore, instead of providing the window member 32 in the mask member 34, the window member 32 is formed as a simple through hole. It is also possible to configure a unit.

In the present embodiment, the interference fringes generated by the optical interference between the 0th-order diffracted light of the object light and the -1st-order diffracted light of the reference light emitted obliquely upward from the second diffraction grating 14 are used as interference fringe observation screens. 18, the interference fringes generated by the light interference between the + 1st-order diffracted light of the object light emitted from the second diffraction grating 14 in the horizontal direction and the 0th-order diffracted light of the reference light are used as interference fringe observation screens. 18 may be formed.

Further, in the present embodiment, the case where the first and second diffraction gratings 12 and 14 consist of two sets of diffraction gratings 12A and 12B and 14A and 14B having different grating constants has been described. May be used. In this manner, three or more interference fringe observation light beams having different measurement sensitivities can be obtained.

Next, a second embodiment of the present invention will be described.

FIG. 4 is a side view showing the oblique incidence interferometer device 10 according to the present embodiment, and FIG. 5 is a side sectional view showing the interference fringe observation light beam selecting means 30 in detail. As shown in these drawings, the oblique incidence interferometer device 10 according to the present embodiment is different from the first embodiment in the configuration of the interference fringe observation light beam selecting means 30.

That is, the light beam selecting means 30 for observing interference fringes of the present embodiment uses the turret mechanism 74 for rotating the mask member 34 about the rotation axis 72 because the mask member 34 is formed in a turret shape. Have been. Then, the turret mechanism 74 is driven to drive the mask member 34.
Is rotated by a predetermined angle around the rotation axis 72, thereby moving the window member 32 to a position where only one of the interference fringe observation light fluxes A and B is transmitted. Selection switching is performed. The mask member 34 is attached to the rotating shaft 72 so as to be non-parallel to the folding mirror 26, so that the light reflected by the window member 32 is excluded from the optical path of the interference fringe observation light beam. .

Further, as shown in FIG.
Are provided with a pair of notches 3 at a predetermined angular interval
In the vicinity of the outer peripheral edge of the mask member 34, a click ball 76 that engages with the notch 34a when the mask member 34 reaches a predetermined rotation angle position is provided. The click ball 76 selectively positions the window member 32 on the optical path of the interference fringe observation light beam A or B.

By adopting the configuration of this embodiment, the same operation and effect as those of the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described.

FIG. 7 is a side sectional view showing in detail the interference fringe observation light beam selecting means 30 of the oblique incidence interferometer apparatus according to this embodiment. As shown in these drawings, the oblique incidence interferometer device 10 according to the present embodiment is different from the first embodiment in the configuration of the interference fringe observation light beam selecting means 30.

That is, the light beam selecting means 30 for interference fringe observation of the present embodiment is provided with a pair of liquid crystal shutters 82A and 82B in the opening 48b formed in the upper surface 48a of the cover member 48 of the dustproof housing 42. The mask member 84 is fixedly supported. These liquid crystal shutters 82A, 82B
Are provided on the respective optical paths of the interference fringe observation light fluxes A and B, and are alternately turned on and off by driving means (not shown). Then, the light flux A for interference fringe observation is always used by one of the liquid crystal shutters.
Only one of B is made to enter the turning mirror 26. The mask member 84 is attached to the cover member 48 so as to be non-parallel to the folding mirror 26, so that the liquid crystal shutter 82A,
The light reflected at 82B is removed from the optical path of the light beam for interference fringe observation.

By adopting the configuration of this embodiment, the same operation and effect as those of the first embodiment can be obtained. In addition, in the present embodiment, since a moving mechanism for mechanically moving the mask member 84 is not required, the above-described operation and effect can be obtained with an extremely simple configuration.

[0047]

The oblique incidence interferometer apparatus according to the present invention causes an interference fringe observation screen to form interference fringes caused by optical interference between object light and reference light emitted in the same direction from the wavefront combining means. However, since the wavefront dividing means and the wavefront synthesizing means are composed of a plurality of sets of diffraction gratings having different grating constants, a plurality of sets of interference fringe observation light beams having different measurement sensitivities can be obtained. The imaging optical system for forming interference fringes on the interference fringe observation screen includes a folding mirror that reverses the interference fringe observation light beam in order to reduce the overall length of the apparatus. ,
By the interference fringe observation light beam selecting means, only a predetermined interference fringe observation light beam out of the plurality of sets of interference fringe observation light beams can be incident. It is possible to form only interference fringes due to the obtained interference fringe observation light beam.

Therefore, according to the present invention, it is possible to observe interference fringes with different sensitivities in a grazing incidence interferometer apparatus having a folding mirror for reversing a light beam for interference fringe observation.

[Brief description of the drawings]

FIG. 1 is a side view showing an oblique incidence interferometer apparatus according to a first embodiment of the present invention.

FIG. 2 is a plan view showing the grazing incidence interferometer shown in FIG.

FIG. 3 is a side sectional view showing a light beam selecting unit for observing interference fringes of the oblique incidence interferometer apparatus shown in FIG. 1;

FIG. 4 is a side view showing an oblique incidence interferometer apparatus according to a second embodiment of the present invention.

5 is a side sectional view showing a light beam selecting unit for observing interference fringes of the oblique incidence interferometer apparatus shown in FIG. 2;

6 is a side sectional view showing the light beam selecting means for observing interference fringes shown in FIG. 2 when viewed from another direction.

FIG. 7 is a side sectional view showing a light beam selecting unit for observing interference fringes of an oblique incidence interferometer apparatus according to a third embodiment of the present invention.

FIG. 8 is a side view showing a conventional example.

FIG. 9 is a side view showing another conventional example.

FIG. 10 is a side view showing still another conventional example.

[Explanation of symbols]

 2 object 2a object surface 10 oblique incidence interferometer 12 first diffraction grating (wavefront splitting means) 12A, 12B diffraction grating 14 second diffraction grating (wavefront synthesis means) 14A, 14B diffraction grating 16 object support member 18 interference Fringe observation screen 20 Imaging optical system 22 Imaging lens 24 Deflection mirror 26 Folding mirror 28 Polarization half mirror (half mirror) 30 Interference fringe observation light beam selecting means 32 Window member (light transmitting part) (1/4 wavelength plate) 34 Mask member 34a Notch 36, 38 Mirror 40 TV camera 42 Dustproof housing 44 Substrate 46 Seal member 48 Cover member 48a Upper surface 48b Opening 50 Spherical fulcrum member 52 Retainer 54 Support plate 56 Adjusting screw 58 Tension spring 60 Slider mechanism ( (Movement mechanism) 62 Guide member 72 Rotary shaft 74 Turret mechanism (Movement machine) ) 76 click ball 82A, 82B liquid crystal shutter 84 mask member A, B interference fringe observation light beam

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Chihiro Furuhata 1-7-39 Kamo-cho, Okaya-shi, Nagano F-term in Okaya Fujikoki Co., Ltd. 2F064 AA09 BB07 CC10 EE10 FF01 GG12 GG13 GG22 GG23 GG38 GG49 GG59 HH08 2F065 AA50 BB26 DD13 EE08 FF04 FF48 FF52 GG04 HH03 HH12 JJ03 JJ26 LL04 LL12 LL30 LL36 LL37 LL42 LL46 PP23 TT01 UU07

Claims (10)

[Claims] 1. Coherent light is made incident on a wavefront splitting means, and
Wavefront division in one direction, one of the light beams is made obliquely incident on the surface to be measured, its reflected light is used as object light, and the other light beam is used as reference light, and these object light and reference light are used as wavefront combining means. And oblique incidence interference configured to form, on an interference fringe observation screen, an interference fringe generated by optical interference between the object light and the reference light emitted from the wavefront synthesizing means in the same direction. An imaging optical system for forming the interference fringes on the interference fringe observation screen, a folding mirror for reversely moving the interference fringe observation light beam emitted in the same direction, and the folding mirror and the wavefront combining. Between the imaging lens and the wavefront synthesizing means, the imaging lens being provided so as to position first and second focal points on the test surface and the return mirror. A half mirror for deflecting and reflecting at least a part of the backward light from the return mirror, wherein the interference fringe observation screen is conjugated to the test surface in a deflecting and reflecting optical path from the half mirror. Wherein the wavefront splitting means and the wavefront synthesizing means comprise a plurality of sets of diffraction gratings having different grating constants, and the plurality of sets of diffraction gratings are provided on the imaging lens side of the folding mirror. An oblique incidence interferometer device comprising: an interference fringe observation light beam selecting means for selectively transmitting only an interference fringe observation light beam formed by a diffraction grating having a predetermined lattice constant. 2. A light beam selecting means for observing interference fringes, comprising: a mask member having a light transmitting portion; and a light transmitting portion on the optical path of the light beam for observing interference fringes formed by a diffraction grating having a predetermined lattice constant. 2. The oblique incidence interferometer according to claim 1, further comprising a moving mechanism for moving the mask member so that the mask member is located at a position corresponding to the oblique incidence. 3. The light transmission unit according to claim 2, wherein the light transmission unit comprises a window member that transmits the interference fringe observation light flux.
An oblique incidence interferometer device as described. 4. The oblique incidence interferometer apparatus according to claim 3, wherein said half mirror comprises a polarization half mirror, and said window member comprises a quarter-wave plate. 5. The oblique incidence interferometer according to claim 3, wherein the window member is arranged non-parallel to the folding mirror. 6. The oblique incidence interferometer according to claim 2, wherein the moving mechanism comprises a turret mechanism for rotating the mask member. 7. The oblique incidence interferometer according to claim 2, wherein the moving mechanism comprises a slider mechanism for reciprocating the mask member. 8. A half-mirror comprising a polarizing half-mirror, wherein said interference-fringe-observing light beam selecting means includes a liquid crystal shutter on an optical path of an interference-fringe-observing light beam formed by each of said plurality of sets of diffraction gratings. The oblique incidence interferometer device according to claim 1, wherein the oblique incidence interferometer device comprises a mask member provided with: 9. The liquid crystal shutter according to claim 8, wherein the liquid crystal shutter is arranged non-parallel to the folding mirror.
An oblique incidence interferometer device as described. 10. The imaging lens according to claim 1, wherein the imaging lens is a single lens that transmits all the interference fringe observation light beams formed by each of the plurality of sets of diffraction gratings. An oblique incidence interferometer device according to any of the above.